It has been recognized for some time that vigorous brushing of the teeth with excessive force can cause damage to tooth material and to gum tissue. Consequently there have been attempts in the prior art to produce toothbrushes that yield in response to excessive manual force on the handle. For example, some prior art toothbrushes have a flexible neck located between the brush end and the handle end. The flexible neck bends in response to increased force applied on the handle, thereby distorting the brush shape. For effective cleaning of the teeth, some amount of pressure needs to be applied to the brush bristles from the handle. With flexible neck toothbrushes the flexible neck acts as a spring, transmitting whatever force is applied at the handle, but offering no clear indication of what is considered to be an excessive force. Furthermore, bending of the toothbrush makes it annoying to use, and the accompanying loss of toothbrush control can itself result in tissue damage.
Attempts to overcome the problems of flexible neck toothbrushes include toothbrushes having complex battery operated light systems signalling excessive handle force, and toothbrush handles which buckle when a predetermined force is reached. Such toothbrushes have their own problems. Battery operated systems result in excessive toothbrush cost. Buckling of plastic toothbrush handles may result in material fatigue where the predetermined force gradually changes over the life of the brush or the buckling member fails. Alternatively, expensive toothbrush materials and construction often result when attempting to minimize such performance limitations.
The level of "excessive" brushing force may vary from one individual to the next, depending on age and condition of the gums at the time. Those prior art toothbrushes, which actually indicate an excessive force, generally indicate only one predetermined force. Also, they are designed to flex or buckle whenever they undergo force application. That is, the force-indicating feature cannot be locked out for greater toothbrush rigidity for traveling, for example, to avoid damage to delicate toothbrush parts.
An object of the present invention is to provide a force-indicating toothbrush which is user adjustable within a range of reasonable brush force levels, such that once a predetermined force is selected, it is repeatable over the life of the brush.
Another object of the present invention is to provide a means for locking out the force-indicating feature when desirable.
A further object of the present invention is to provide a force-indicating toothbrush which can be made inexpensively from common materials and which provides both a tactile and an audible indicator of excessive force.
Yet another object of the present invention is to provide a force-indicating toothbrush which can have its brush member and handle molded as one piece.